When upgrading any 1.18.2 world to 1.19 the end generates with weird chunk borders likely caused by the world blending. Since I created this world just to check if it wasn't a modded issue i can confirm this was done 100% vanilla

To recreate:

make a new world in 1.18.2

Go to the end and fly to the  outer islands or /kill the dragon and go through the portal

Fly around a bit to load chunks

Quit Minecraft and start Minecraft in 1.19

Go to where the world would upgrade terrain (generate new chunks)